Evaluation of fungicide programs for control of apple scab apple scab on ‘Jerseymac’ apples in 2012

摘要

A trial was conducted at the New York State Agricultural Experiment Station in Geneva, NY to evaluate the effectiveness of dodine programs in an orchard with scab that had formerly become resistant to dodine. The orchard site is a mature planting of 4-yr-old ‘Jerseymac’ trees on B.9 rootstocks. Treatments were applied dilute (300 gal/A) to drip using a handgun (300 PSI) at 7-10 day intervals (14 Mar-green tip, 21 Mar-half-inch green, 28 Mar-tight cluster, 4 Apr-pink; 13 Apr-early bloom, 20 Apr-latebloom, 30 Apr-petal fall, 10 May-1st cover, 24 May-2nd cover). The first three applications of certain Syllit programs (see Table 1.) were made 48 hours after the first three infection periods before returning the standard calendar schedule. Summer cover sprays (3rd through 6th cover) were applied to all programs with an airblast sprayer at 3X concentration. Apple scab infection events based on Mills predictions using estimated leaf wetness occurred 18 Mar, 24 Mar, 31 Mar, 21 Apr, 30 Apr, 2 May, 7 May.Eleven additional infection events occurred between 3rd and 6th cover. The incidence of apple scab symptoms on ‘Jerseymac’ was assessed for cluster leaves and young fruit on 19 Jun, and for terminal leaves on 26 Jun. The incidence of apple scab on cluster leaves was expressed as a percentage calculated from the number of cluster leaves with scab lesions out of the total number of cluster leaves with 10 clusters assessed for four replicate trees per treatment. The incidence of apple scab symptoms on terminal leaves was calculated as the number of terminal leaves with apple scab lesions out of eight fully expanded leaves counted from the distal end of the shoot. For each of four treatment replications, the incidence of 10 shoots was assessed. The incidence of apple scab symptoms on fruit was calculated from the number of fruit with apple scab lesions out of five randomly collected fruit. For each of four treatment replications, 10 such samples were assessed. Disease incidence data was subject to analysis of variance (ANOVA) for a randomized block design using accepted statistical procedures and software (e.g. Mixed Models (MIXED)) procedure of SAS (version 9.3; SAS Institute Inc., Cary, NC). All percentage data was subject to arcsine square root transformation prior to analysis.